It is common when testing materials to undertake tensile tests of materials by forming a standard sample, marking the sample with one or more datum points and applying an increasing load to the sample while monitoring movement of the datum point or points. It is known to utilise video cameras for the purposes of monitoring the movement and by using a suitable mathematical algorithm, the distance between the marks can be determined. This technique results in an apparatus which is reliable and cost effective. However, there is a demand for more accurate measurement techniques which can currently only be satisfied with expensive equipment.
Two prior disclosures, GB 2205396A and GB 2223319A, are both relevant in describing the technology which already exists in the field of the present invention. Both these documents describe an arrangement wherein the sample to be tested is contained in an environmentally controlled test chamber and viewed through a transparent window. As the sample is located within the test chamber, problems may exist due to the need to view the sample through a window and further the environment between the camera and the window is different to the environment within the test chamber.